Three minutes before midnight on March 12, 1928, the St. Francis Dam catastrophically failed. There were no eyewitnesses to the dam's collapse, but a motorcyclist named Ace Hopewell rode past the dam and reported feeling a rumbling and the sound of "crashing, falling blocks," after riding about a half-mile (800 m) upstream. He assumed this was either an earthquake or another one of the landslides common to the area, not realizing he was the last person to have seen the St. Francis Dam intact, and survive.
Dam keeper Harnischfeger and his family were, most likely, the first casualties caught in the floodwave, which was at least 125 ft (38 m) high when it hit their cottage in San Francisquito Canyon, approximately 1/4 mile (400 m) downstream from the dam. Forty-five minutes before the collapse, Hopewell, the motorcyclist, also reported seeing a light in the canyon below the dam—the dam itself did not have lights—suggesting Harnischfeger may have been inspecting the dam immediately prior to its failure. The body of Harnischfeger's wife was found fully clothed and wedged between two blocks of concrete near the broken base of the dam; their six-year-old son's body was found farther downstream, but Tony Harnischfeger's body was never found.
As the dam collapsed, twelve billion U.S. gallons (45 billion liters) of water surged down San Francisquito Canyon in a floodwave, demolishing the heavy concrete walls of Power Station Number Two (a hydroelectric power plant), and destroying everything else in its path. The flood traveled south down San Francisquito Canyon, flooding parts of present-day Valencia and Newhall. The deluge then turned west into the Santa Clara River bed, flooding the towns of Castaic Junction, Fillmore, and Bardsdale. The flood continued west through Santa Paula in Ventura County, emptying its victims and debris into the Pacific Ocean at Montalvo, 54 miles (87 km) from the reservoir and dam site. When it reached the ocean at 5:30 a.m., the flood was almost two miles (3 km) wide, traveling at a speed of 5 miles (8 km) per hour. Bodies of victims were recovered from the Pacific Ocean, some as far south as the Mexican border.
Was talking with the Chimney repair guy up here about this the other day. Pretty interesting story. Here is a NPR story about it The St. Francis Dam Disaster on NPR as well.